1. Field of the Invention
The present invention relates generally to semiconductor devices that include an organic field effect transistor (OFET). More particularly, the present invention relates to organic semiconductor devices that utilize vertical device architecture to form a vertical organic field effect transistor (VOT).
2. Description of Related Art
The publications and other reference materials referred to herein to describe the background of the invention and to provide additional detail regarding its practice are hereby incorporated by reference. For convenience, the reference materials are numerically referenced and grouped in the appended bibliography.
Organic field effect transistors (OFETs) have attracted considerable attention since their discovery [1,2] due to their flexibility, their low cost, and their amenability to fabrication over large surface areas. They have been extensively investigated [3,4]. However, the performance of OFETs remains poor compared to their inorganic counterparts. The reduced performance of the OFETS with regards their much lower current output (on the order of μA) and higher working voltages (up to 100 V), is due to the much lower carrier mobility for organic materials compared to the carrier mobility of materials found in inorganic FETs [4,5]. Several approaches have been used for improving the performance of these devices.
In order to circumvent the low carrier mobility problem, decreasing the channel length and increasing the dielectric constant of the gate insulators of the OFETs were approaches tried by several research groups. Dimitrakopoulos, et al, reported low working voltage OFETs using high dielectric constant metal oxide as the gate insulator; however, the source-drain current was still low [6]. The method for decreasing the channel length of OFETs was to employ a vertical structure for device fabrication. Several groups utilized and reported this approach [7,8]. In the vertically structured transistor the gate electrode was located between and perpendicular to the source and the drain electrodes. The cross sectional area for the source-drain current of these vertical transistors was determined by the channel width (which was in the micrometer range) multiplied by the channel thickness (which was several monolayers) [9,10]. This cross sectional area was the same as that found for non-vertical OFETs [4]. The key point was that the small cross section of the channel in OFETs limited their current output.
High current output and low working voltage OFETs are highly desired for many applications such as active-matrix flat panel displays [11].